Separation of suspended matter from liquid is known in the art. Methods such as precipitation, centrifugation and filtering are commonly used for separation purposes in a vast number of industries including chemical and bioprocess industry. The latter separation method is relevant for the present invention.
Several problems concerning the separation of suspended matter from liquid exist, most significantly the blocking of the filter material used that requires replacement of filters, prolong filtration cycles, use of additional containers and eventually high cost. In those instances where the suspended material is a biological entity, the current methods include either centrifugation of the suspended entities or the use of cross-flow filtration methods to reduce the volume, both of which are cumbersome, require large vessels for receiving the filtrate and frequently strain the material contained in the solution causing significant decrease in the productivity of the process.
Centrifugation is a very expensive separation method. When filtering liquids having a high suspended matter content there are significant problems concerning accumulation of suspended matter on the filter. This accumulation is known as the filter cake. In conventional methods the filter cake will grow until further filtering is impossible and the filter then has to be cleaned. There are various techniques for limiting the filter cake. One such technique is cross-flow. Here, the filter is kept clean by continuously scrubbing it with high-speed gas bubbles.
Another filtering method is back flushing. Here, the movement of the suspension is reversed to lift the filter cake from the filter. When using the cross-flow or back flushing methods the filter cake is not accumulated on the filter but is accumulated in the suspension. This requires the filtering process to be either stopped or for the existence of an outlet for the accumulated suspended matter. In the latter situation the removed suspended matter will still have a relatively high liquid content.
A further filtering method is flushing. The filtering process is stopped and the filter is washed. Here, the suspended matter is accompanied by a lot of liquid.
The above problems are overcome by the present invention by presenting a method and an apparatus capable of continuously removing suspended matter from a liquid, and thereby provide a method and apparatus capable of operating continuously without getting and at the same time having an increased filtering capacity and a economical advantage over the prior art.